1. Field of the Invention
The present invention relates to a copier, printer, facsimile apparatus or similar image forming apparatus and more particularly to a sheet finisher operatively connected to the image forming apparatus for executing preselected processing with sheets.
2. Description of the Background Art
A sheet finisher is proposed in various forms in the past and capable of stapling, punching or otherwise processing sheets sequentially driven out of an image forming apparatus. The prerequisite with a sheet finisher of the type jogging sheets one by one and then stapling them together is the accuracy of jogging. Various methods have heretofore been proposed for meeting such a prerequisite.
It is a common practice to jog sheets with a pair of jogger fences or similar jogging members. Many of conventional jogging members address to accurate jogging at or around the allowable limit of the number of sheets that can be dealt with by, e.g., a stapler. Many users, however, daily deal with a stack of ten sheets or less to be stapled together and rarely deals with a stack of fifty sheets or more, as known by experiment and proved by the results of various market researches. More specifically, accurate jogging of a small number of sheets impresses users favorably.
Generally, jogging of sheets becomes more difficult as the number of sheets to be stapled together increases. In light of this, the jogging members are moved toward each other to a distance slightly smaller than the width of sheets, thereby pressing the edges of a sheet stack. This kind of scheme is desirable when the number of sheets is small. However, as the number of sheets sequentially stacked increases, it becomes difficult for the sheets to move. This, coupled with an increase in the reaction of the sheets acting on the jogging members, causes not only the jogging members but also parts for driving them to bend, obstructing accurate jogging.
Another advantage achievable with the jogging members pressing a sheet stack, as stated above, is that they absorb irregularity in sheet width and loosens sheets being stacked for thereby enhancing accurate jogging.
Japanese Patent No. 2,960,770 teaches a sheet finisher of the type described. After the last sheet has been stacked and jogged, the sheet finisher taught in the above document causes jogging means to again move in order to press the sheet stack during stapling. With this configuration, the sheet finisher prevents the jogged sheets from moving during stapling. The sheet finisher, however, presses the sheet stack by the same amount during stapling as during jogging. This is because the sheet finisher addresses to accurate jogging at or around the allowable limit of the number of sheets, as stated above, and directed only toward the simplification of software.
When a large number of sheets are to be stapled, the jogging means taught in the above document again moves after the last jogging movement so as to press the sheets during stapling. This desirably maintains the sheets in the accurately jogged position even during stapling. However, when the number of sheets to be stapled together is small, the sheets are loosened and therefore bent. As a result, the sheets stacked together are apt to shift in the lengthwise direction, which is perpendicular to the direction in which the jogging means moves.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 2000-191219.
It is an object of the present invention to provide a sheet finisher for an image forming apparatus capable of accurately jogging sheets without regard to the number of sheets.
In accordance with the present invention, a sheet finisher includes a stacking section for stacking sheets thereon, a jogging device for jogging the sheets sequentially stacked on the stacking section one by one, and a processing device for executing preselected processing with the sheets. The jogging device includes a pair of jogging members for jogging the sheets one by one, and a controller for controlling the jogging members. The controller moves, in accordance with the width of the sheets in a direction perpendicular to the direction of sheet conveyance, each jogging member to a first position remote from one edge of the sheets in the direction of width by a preselected amount, a second position closer to the edge than the first position by a preselected amount and slightly overlapping the edge, and a third position where, when the processing device executes the preselected processing, the jogging member substantially contacts the edge in accordance with the width. Assuming that the jogging members are spaced from each other by a distance of L2 at the second position or by a distance of L3 at the third position, the controller sets at least one of the distances L2 and L3 in accordance with the width or the number of the sheets.
An image forming system including the above sheet finisher and an image forming apparatus are also disclosed.